would it be a good idea to not rub anything containing tiny bits of silica on my cutting boards, where it may meet with my knife blades?

silica vs. knife blade: silica wins.

i have to also imagine that this can't be good for anyone's teeth.

there's a few more places i need to look for table salt without the silica. in the meantime, are there any alternate suggestions?

Silicon dioxide? You mean as in SAND??

Use table salt. The reason salt is used to disinfect wood cutting boards, is that it is hygroscopic, soluble in water, and it acts to dehydrate cells. Silicon dioxide [sand] only gets wet and probably has little effect on bacterial cell walls.